The growing demands on mobile networks to support data applications at higher throughputs and spectral efficiencies have driven the need to develop Orthogonal Frequency Division Multiplexing (OFDM) based 4th generation (4G) networks including third generation partnership project, 3GPP, Long Term Evolution (LTE) networks. Because of the scarcity of spectrum, the same frequencies are reused at all cell sites. The resulting interference limited system will not achieve the full potential capacity that the LTE standard can support without the implementation of one or more interference mitigation and or cancellation techniques. Interference mitigation and/or cancellation techniques have been investigated and deployed with varying degrees of success in mobile networks for over 20 years. Traditional approaches have focused on ensuring orthogonality between transmitted signals in time or frequency. Other systems operate spatially or by actively removing and cancelling interfering signals from the desired signal.
In early second generation, 2G, cellular systems, orthogonality was achieved primarily through static pre-planned allocations of radio resources. Third generation, 3G, systems introduced interference cancellation techniques based mostly on a combination of blind information gathered at a base station such as spectrum usage monitoring and coarse exchange of interference indicators such as the Rise over Thermal (RoT) indicator employed in the 3GPP 1xEV-DO standard. Typically interfering signals have been estimated using blind detection and their estimates subtracted from the desired signals.
In 4G networks, the advanced evolution of LTE has focused on Coordinated Multipoint (CoMP) as a means to improve performance of the air interface. The central concept of Uplink Coordinated Multipoint (UL CoMP) is that although a user equipment, UE, is served by one cell, the neighboring cells may receive the UE's signal with sufficient quality such that they may be able to contribute to the reception of the UE's signal.
A fundamental problem of UL-CoMP is the cost and complexity of the needed transport network required to deliver signals between cells. One solution involves transporting digitized RF spectrum signals from the radios of neighboring cells. This requires a bandwidth on the order of 2.5 Gbps per 2 branch diversity 20 MHz carrier. After provisions are made to allow multiple cells to share with neighboring cells, the amount of required inter cellular bandwidth easily exceeds the non-CoMP case by a factor of 20 to 40 times. Only a very limited number of operators, those having a very favorable transport cost model, can afford to ubiquitously deploy a system having such a heavy backhaul capacity.